GeneWeb - Consanguinity

This part explains the concepts of "consanguinity" and "relationship"
used by GeneWeb and how they are computed.

Consanguinity and Relationship

The genom of an individual consists of a great number of genes which,
if mutations are ignored, reproduce identically. The genes can be used
to measure the identity of a person.

The genes are placed in precise locations named "locus". Each
individual has for each locus two genes, one transmitted by his
mother, the other by his father, and transmits to his children a copy
of the one of his genes.

The Consanguinity of an individual x is the
probability cg(x) to find in a given locus two identical
genes.

The Relationship of two individuals x and y
is the probability pr(x, y) to find in the same locus two
identical genes.

Computations

A probability calculus shows that:

The consanguinity cg(x) is equal to the relationship
pr(px,mx) of the parents px and mx of
x.

If x..a..y is a minimal relationship link between
x and y (i.e. such as the branches x..a and
a..y have just a in common), then it contributes to
the relationship of x and y of a factor:

1
---- (1 + cg a)
n+1
2

where n is the length (distance x..a + distance
a..y) of the relationship link x..a..y.

The relationship of x and y is the sum of the
contributions of all their minimal relationship links.

GeneWeb

GeneWeb displays the consanguinity and the relationship in
the form of a percentage.

Statistically, on the great number of locuses of an individual, the
consanguinity corresponds approximately to the percentage of his
locuses holding identical genes.

The algorithms of consanguinity and relationship were written by
Didier Rémy, director of research at INRIA. We thank him for
that.